The present invention relates generally to turbine engines and more specifically to protective devices for turbine engines that prevent debris from entering the engine, and to smooth turbulent air flow.
Turbine engines produce thrust by increasing the velocity of the air flowing through the engine. A turbine engine consists primarily of an air inlet, compressor, combustion chamber or chambers, turbine section, and exhaust. There are several different types of turbine engines, but all turbine engines have some parts in common. All turbine engines have an inlet to bring free stream air into the engine. The inlet sits upstream of the compressor and its design is an important factor in engine net thrust or power.
The total pressure through the inlet may be reduced because of several flow effects. Aerodynamicists characterize the inlet's pressure performance by the inlet total pressure recovery, which measures the amount of free stream flow conditions that are recovered. The pressure recovery depends on a wide variety of factors, including the shape of the inlet, the speed of the aircraft, the air flow demands of the engine, and aircraft maneuvers.
As air is brought from free stream to the compressor face, the flow may be distorted by the inlet. At the compressor face, one portion of the flow may have a higher velocity or higher pressure than another portion. The flow may be swirling, or some section of the boundary layer may be thicker than another section because of the inlet shape. The rotor blades of the compressor rotate around the central shaft. As the blades encounter distorted inlet flow, the flow conditions around the blade change very quickly. The changing flow conditions can cause flow separation in the compressor, a compressor stall, and can cause structural problems for the compressor blades.
Due to the design and function of a turbine engine's air inlet, the possibility of ingestion of debris always exists. This causes significant damage, particularly to the compressor. When this occurs, it is called foreign object damage (FOD). Typical FOD consists of small nicks and dents caused by ingestion of small objects from the ramp, taxiway, or runway. However, FOD damage caused by bird strikes or ice ingestion can also occur, and may result in total destruction of an engine. Prevention of FOD is a high priority in aircraft safety.
Typically, turbine engines have an air intake inlet opening also referred to as an inlet duct, the front portion of which comprises an air intake opening lip (or “lipskin”) to, among other things, protect the leading edge of the air intake opening. The center of the engine, however, remains open and accessible to birds, wildlife and other foreign object debris damage, including even possible terrorist threats. In addition, a vortex pattern of turbulent air is caused, partially by air flow over the lipskin in several directions, which causes sand, gravel and small objects to be ingested into the engine and causes lower engine efficiency.
Engine protection devices have been proposed, which substantially comprise a shroud surrounding the engine component and fitted to a fixed supporting member of the engine component. Many propose a construction of metals, such as steel, which must be particularly thick and heavy. Such shrouds are therefore unsatisfactory, by increasing the overall weight of the aircraft and so impairing performance and increasing fuel consumption. In the case of inlet covers, such as screens, they have been found to produce a safety hazard when ice forms over the screen. They also can impair the efficiency of the engine by interfering with normal air flow through the engine. It has also been proposed to activate or retract such protection devices by mechanical or explosive actuators, reacting to sensors that have been installed in the craft's nose cone. This complexity renders such designs unpractical for most aircraft. A turbine engine protection device that avoids these disadvantages is thus highly desirable.